Insertion tool for use with trial intervertebral distraction spacers

ABSTRACT

A trial spacer kit has a plurality of trial spacers of varying heights. Each spacer includes a disc having a top surface and a bottom surface defining a height of said spacer, an annular groove formed in said disc that defines a central trunk of said spacer, the central trunk extending between the top and bottom surfaces of said spacer, a first radial flange provided at an upper end of the central trunk and a second radial flange provided at a lower end of the central trunk. The annular grooves of the spacers have a common dimension. The radial flanges of a first one of the spacers is thicker than the radial flanges of a second one of the spacers so that the first one of the spacers has a greater height than the second one of the spacers.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/115,751, filed Apr. 3, 2002, now U.S. Pat. No. 6,855,151,which is a continuation of U.S. patent application Ser. No. 09/906,120,filed Jul. 16, 2001, now U.S. Pat. No. 6,428,544, the disclosures ofwhich are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates generally to a treatment for scoliosis and morespecifically to the instruments, implants, distracting trial spacers,and surgical methodology used in the treatment and correction ofscoliosis. The bones and connective tissue of an adult human spinalcolumn consists of more than 20 discrete bones. These more than 20 bonesare anatomically categorized as being members of one of fourclassifications: cervical, thoracic, lumbar, or sacral. They are coupledsequentially to one another by tri-joint complexes that consist of ananterior intervertebral disc and the two posterior facet joints. Theanterior intervertebral discs of adjacent bones are cushioning cartilagespacers.

The spinal column of bones is highly complex in that it includes these20 bones coupled to one another (and others), and it houses and protectscritical elements of the nervous system having innumerable peripheralnerves and circulatory bodies in close proximity. In spite of thesecomplications, the spine is a highly flexible structure, capable of ahigh degree of curvature and twist in nearly every direction.

Genetic, congenital and/or developmental irregularities are theprinciple causes that can result in spinal pathologies in which thenatural curvature of the spine lost. Scoliosis is a very common one ofthese types of irregularities, resulting in a sequential misalignment ofthe bones and intervertebral discs of the spine. Major causes ofscoliosis are idiopathic (i.e., unknown cause), congenital developmentalanomalies and neuromuscular disorders such as cerebral palsy. Themisalignment usually manifests itself in an asymmetry of the vertebralbodies, such that, over a sequence of spinal bones, the spine twistsand/or bends to one side. In severe cases, neurological impairmentand/or physiological disability may result.

The present surgical technique for treating scoliosis (as well as otherspinal conditions) includes the implantation of a plurality of hooksand/or screws into the spinal bones, connecting rods to these elements,physically bracing the bones into the desired positions, and permittingthe bones to fuse across the entire assembly. This immobilization oftenrequires anterior plates, rods and screws and posterior rods, hooksand/or screws. Alternatively, spacer elements are positioned between thesequential bones, which spacers are often designed to permit fusion ofthe bone into the matrix of the spacer from either end, hastening thenecessary rigidity of the developing bone structure. Spacers allow bonefusion to grow into or around them. There are two classes ofintervertebral spacers: horizontal cages such as the BAK.TM. and Raycages, as described and set forth in exemplary U.S. Pat. No. 5,015,247to Michelson and U.S. Pat. No. 5,026,373 to Ray et al., respectively,and vertical cages such the Harms cages, as described and set forth inexemplary U.S. Pat. No. 4,820,305.

Similar techniques have been employed in other spinal infirmities,including collapsed disc spaces (failure of the intervertebral disc),traumatic fractures, and other degenerative disorders. While the presentinvention has many applications, such applications include the treatmentof any spinal disorder in which the space between vertebral bones needsto be surgically separated (the bones distracted), realigned and thenfused to one another.

A variety of systems have been disclosed in the art which achieveimmobilization and/or fusion of adjacent bones by implanting artificialassemblies in or on the spinal column. The region of the back that needsto be immobilized, as well as the individual variations in anatomy,determine the appropriate surgical protocol and implantation assembly.With respect to the failure of the intervertebral disc, and theinsertion of implants and/or height restorative devices, several methodsand devices have been disclosed in the prior art.

Restoring the appropriate height and orientation of the vertebral bonesand the intervertebral space is the first step in the surgical strategyfor correcting this condition. Once this is achieved, one class ofsurgical implantation procedures involves positioning a device into theintervening space. This may be done through a posterior approach, alateral approach, or an anterior approach. Various implant devices forthis purpose include femoral ring allograft, cylindrical metallicdevices (i.e., cages), and metal mesh structures that may be filled withsuitable bone graft materials. Some of these implant devices are onlysuitable for one direction of approach to the spine. All of thesedevices, however, are provided with the intention that the adjacentbones will, once restored to their appropriate alignment and separation,then grow together across the space and fuse together (or at least fuseinto the device implanted between the bones).

Most recently, the development of non-fusion implant devices, whichpurport to permit continued natural movement in the tri-joint complexhave provided great promise. The instrumentation and methods for theimplantation of these non-fusion devices, as well as the implantation ofthe fusion devices catalogued previously, therefore should integrate thefunctions of restoring proper anatomical spacing and easy insertion ofthe selected device into the formed volume.

It is, therefore, an object of the present invention to provide a newand novel treatment for scoliosis, as well as for the treatment ofspinal pathologies in general.

It is, correspondingly, another object of the present invention toprovide an intervertebral distraction trial tool which more accuratelyand easily separates collapsed intervertebral spaces.

It is further an object of the present invention to provide anintervertebral distraction trial tool which more can be used to correctscoliosis and/or restore normal alignment to the spine.

It is further an object of the present invention to provide aninstrument that proficiently and simply manages the insertion, rotation,and removal of the intervertebral distraction trial tools.

It is further an object of the present invention to provide animplantable spacer device that permits more anatomically appropriate andrapidly osteogenic fusion across the intervertebral space.

Other objects of the present invention not explicitly stated will be setforth and will be more clearly understood in conjunction with thedescriptions of the preferred embodiments disclosed hereafter.

SUMMARY OF THE INVENTION

The present invention is directed to a method of treatment of scoliosisand other spinal disorders. This method of treatment further includesseveral new and novel instruments, implantable trial distractionelements, and intervertebral spacer implants. Inasmuch as thedescription of the new and novel method cannot be complete without adescription of each of these integral members, the following includesample explanation of these elements as well as description of thesurgical techniques.

First, the patient spine is exposed through an anterior approach (i.e.,the surgeon creates an access hole which permits direct interaction withthe anterior and/or anterio-lateral portion of the intervertebralbodies). In the case of scoliosis, as well as in other disorders inwhich the intervertebral space requires distraction and/orrepositioning, the surgeon removes the intervertebral disc material,usually leaving some portion of the annulus (the cylindrical weave offibrous tissue which normally surrounds and constrains the softercartilage cushion of the disc material). The surgeon then, insuccession, inserts a series of intervertebral trial spacers of definedwidth. Each of the series of spacers is of a progressively widerthickness, resulting in the continual widening of the space untilrestoration of the proper disc height has been achieved. Proper discheight restoration is determined by surgical experience, and byobservation of the annulus. (Often, the tightening of the annulusindicates that the proper disc height has been reached, inasmuch as theannulus is much less likely to be distorted by the same disruption thatcaused the intervertebral disc to collapse in the first place.)

More particularly, with respect to the specific instruments disclosedherein, a series of solid trial spacer elements and an instrument fortheir insertion and removal is now provided. Each trial spacer is agenerally cylindrical disc having a deep annular groove at its midpoint,which forms a central trunk and radial flanges at each end of the trunk.Stated alternatively, two cylindrical upper and lower halves of the discare held in a closely coaxial spaced apart association by the centraltrunk, which forms a coaxial bridge between the upper and lower halves.The annular groove is particularly useful for holding the spacer usingthe spacer insertion instrument of the invention, described below, inthat the holding end of the insertion instrument fits within the groove.

A variety of features of embodiments of the trial spacer elements aredisclosed. In some embodiments, such as the first and second embodimentsdescribed below, support portions (the portions that are in contact withthe adjacent vertebral bodies when the spacer is disposed between thebodies) of the top and bottom surfaces are parallel. Spacers having thisfeature are generally described herein as “constant thickness” trialspacers. In other embodiments, such as the third and fourth embodimentsdescribed below, the support portions are not parallel, providing anoverall taper to the spacer at an angle. Spacers having this feature aregenerally described herein as “tapered thickness” trial spacers. Thetapered thickness trial spacers are particularly useful for treatingscoliosis, as described below.

Other features of embodiments of the trial spacer elements includebeveled flanges and non-parallel annular groove walls. Morespecifically, in some embodiments, such as the second and fourthembodiments described below, the flanges are radially beveled in that anouter edge of the top surface of the disc is tapered toward an outeredge of the bottom surface of the disc. In other embodiments, such asthe first and third embodiments described below, the flanges are notradially beveled in this manner. The radial beveling feature can beparticularly useful for easing the insertion of the spacer in betweencollapsed vertebral bodies, as described below. Further, in someembodiments, such as the first and third embodiments described below,the walls of the annular groove are parallel, such that the floor of thegroove is as wide as the opening of the groove. In other embodiments,such as the second and fourth embodiments described below, the walls ofthe annular groove are tapered toward one another with the increasingdepth of the groove, such that the floor of the groove is narrower thanthe opening of the groove. Each type of annular groove is useful,depending on the particular surgical application and on the particularembodiment of the spacer insertion instrument that is used to insert thespacer.

Collections of trial spacer elements are provided by the invention.Preferably, each spacer in a particular set maintains the same diameteras the other spacers in the set. (It shall be understood that differentcollections of spacers may be provided such that the diameter of theselected collection of trial spacers is appropriate for the specificpatient being treated.) Also preferably, each spacer in a particular sethas a predetermined depth that differs from the depth of the otherspacers in the set. The predetermined depth is provided in that whileeach spacer in the set shares the same annular groove dimensions (sothat each can be held by the same insertion instrument), each spacer hasa different flange thickness (in sets where the spacers are constantthickness spacers). For sets of tapered thickness spacers, thepredetermined maximum depth and predetermined minimum depth (the twodepths providing the overall taper) are provided in that while eachspacer in the set shares the same annular groove dimensions (so thateach can be held by the same insertion instrument), each spacer has adifferent maximum flange thickness and a different minimum flangethickness. Preferably in sets of tapered thickness spacers, the overalltaper angle is the same for each spacer in the set. The usefulness ofproviding sets of spacers similar in most respects except for the depthdimension will be described in greater detail below.

With regard to the instrument for the insertion and removal of the trialspacer elements, a first embodiment (particularly useful for insertingconstant thickness trial spacers) of a spacer insertion tool includes anelongated shaft and a handle at one end of the shaft. The distal end ofthe shaft includes semi-circular hook that is adapted to hold a trialspacer within an enclosure formed by the hook. The angle swept out bythe hook is slightly greater than 180 degrees, but the inner diameter ofthe hook is only slightly larger than the central trunk of the trialspacer. Therefore, the trial spacer may be snapped into the enclosure,but maintains complete rotational freedom within its grasp. A loadingtool may be provided to assist in the loading and unloading of the trialspacer from the trial spacer insertion instrument of this embodiment.This loading tool comprises a forked hook having two curved tinesseparated by a notch that engages the shaft of the insertion tool as thetines engage the flanges of the trial spacer, to force the trial spacerinto the enclosure. Alternatively and/or additionally, the same devicemay be utilized to remove the spacer from the enclosure, by reversingthe position of the forked hook relative to the insertion tool and thespacer.

The insertion tool of this embodiment can be used to insert a series ofconstant thickness trial spacers (some of which may have beveled flangeedges for easing the insertion between the collapsed bones and into thespace to be distracted). More specifically, thinner trial spacers caninitially be inserted into the spacer, followed successively by thickertrial spacers until the desired spacing is achieved. Once theappropriate spacing has been achieved, immobilization of the spine byfixation, fusion, or non-fusion techniques and devices, such as thoseset forth in co-pending U.S. patent application Ser. Nos. 09/906,117 and09/906,118, entitled “An Intervertebral Spacer Device Having a WaveWasher Force Restoring Element” and “An Intervertebral Spacer DeviceHaving a Spiral Wave Washer Force Restoring Element”, respectively, aswell as U.S. Pat. No. 5,989,291, entitled “An Intervertebral SpacerDevice”, each of which has been assigned to the same assignee as thepresent invention, the specifications of which are all fullyincorporated herein by reference, may be desirable.

While simple distraction to a constant height across the intervertebralspace is appropriate for standard disc compression pathologies, in thecase of scoliosis, simple constant thickness distraction is insufficientto remediate the pathological condition. What is necessary is thedistraction of the sequence of spaces, each to an appropriate angle andheight, such that the overall spinal configuration is anatomicallycorrect. Tapered trial spacers, such as those disclosed in the presentapplication, are the first such distraction tools to provide such atailored correction of the misangulation of the spinal bones.

More particularly, the surgeon inserts the tapered trial spacers intothe intervertebral space (presumably from the anterior, oranterio-lateral, approach) with the narrow edge of the trial spacerforming a wedge and sliding between the adjacent bones. By utilizingeither a second or third embodiment of the spacer insertion tool,described more fully below, the surgeon may turn the spacer around itsaxis within the intervertebral space to find the most appropriaterotational position (corresponding to the most desirable straighteningeffect on the spinal column). Stated alternatively, each of the taperedtrial spacers has an overall wedge shape that generally corresponds tothe pathological tapering of the adjacent bones that characterizesscoliosis. By rotating the wedge-shaped spacer after it has been placedbetween the adjacent bones, the overall disc alignment may becompensated, restoring appropriate anatomical status. It should beunderstood that additional rotation of the spacer may restore lordosisto the spine, and that over-rotation (if the particular spine isflexible enough) of the spacer would result in a pathological curvaturein the opposite direction.

This second embodiment of the spacer insertion tool includes a handleand an elongated dual shaft, the dual shaft culminating in a trialspacer grasping pincer, rather than the simple hook of the firstembodiment. This pincer differs from the hook of the first embodiment ofthe trial spacer insertion tool described above, inasmuch as the dualshaft includes a fixed shaft and a selectively engagable shaft which,together, form pincer. More specifically, the fixed shaft includes asemicircular hook portion of the pincer at its distal end, having anenclosure within which a trial spacer can be placed. The selectivelyengagable shaft includes the complementary portion of the pincer, whichmoves toward the hook portion to grasp and hold the trial spacer whenthe engagable shaft is engaged, and moves away from the hook portion torelease the trial spacer when the engagable shaft is disengaged. (Thespacer can be unloaded and loaded when the engagable shaft isdisengaged.) The engagement action prevents the spacer from movingrelative to the tool, and therefore permits the surgeon to rotate thetapered spacer in between the vertebral bodies (by contrast, the firstembodiment of the trial spacer insertion instrument permitted the spacerto rotate freely in the enclosure of the hook). There are alternativeinsertion and rotating instruments that may be designed, so long as theyselectively and alternatingly release or hold the trial spacer securelyagainst rotation (the spacer cannot be permitted to rotate freely if itmust be turned in the intervertebral space). The tapered trial spacersthemselves can include angle markers that clearly indicate to thesurgeon the amount of rotation that was necessary for the correction ofthe spinal deformity. Such angle markers can also serve as a guide forthe implantation of a secondary bone graft (e.g., a femoral ring) oranother intervertebral spacer device.

Once the surgeon has determined the appropriate geometry for thesurgical implants via the trial spacers, he or she is ready toimmobilize the spine in that position. While multiple ways forimmobilizing the spine are disclosed in the prior art, any one of whichand others may be suitable for the specific surgical patient'streatment, three alternative ways are herein described.

First, the trial spacers may be left in the patient while rod fixationapparatuses (anterior or posterior) are mounted to the spine, therebyholding the spine in its desired orientation even after the trialspacers are subsequently removed. Alternatively, surface plating and/orintervertebral cage devices may be mounted to the spine to promotefusion without the need for bulky rod assemblies. (While this approachmay seem more surgically desirable, questions regarding the long termstability of these constructs have led some surgeons to chosecombinations of rodding and cages.)

A third approach to immobilizing the corrected spine is to insert ashaped bone graft, or suitably contoured porous metal spacer, into theproperly distracted intervertebral space is described more fully inco-pending U.S. patent application Ser. Nos. 09/844,904 and 09/906,123,respectively entitled “A Porous Interbody Fusion Device HavingIntegrated Polyaxial Locking Interference Screws” and “PorousIntervertebral Distraction Spacers”, assigned to the same assignee asthe present invention, the specifications of each being fullyincorporated herein by reference.

The tapered trial spacers may also serve as precursors (measuringinstruments) for another spacer (e.g., a porous metal spacer), similarlyshaped, which is inserted into the intervertebral space by the sameinstrument.

Therefore, the present invention, in its many embodiments andcomponents, is directed to a surgical treatment for restoring a properanatomical spacing and alignment to vertebral bones of a scoliosispatient. In one desired embodiment, the present invention comprises asurgical method, which in a first embodiment, comprises: 1. determiningan angular misalignment associated with at least one pair of adjacentvertebral bones; 2. sequentially inserting and removing a series ofprogressively wider cylindrical spacer elements into the correspondingintervertebral space between said at least one pair of adjacentvertebral bones until the proper anatomical spacing between the pair ofadjacent vertebral bones is restored; 3. for each intervertebral space,inserting a diametrically tapered cylindrical spacer element into theintervertebral space between said corresponding pair of adjacentvertebral bones; and 4. rotating said diametrically tapered cylindricalspacer element such that the rotational orientation of the taperedcylindrical spacer element introduces the appropriate counter offset tothe intervertebral space of the previously misaligned scolioticvertebral bones, thereby restoring the proper anatomical alignment ofthe vertebral bones.

It shall be understood that each of said progressively wider cylindricalspacer elements includes substantially parallel upper and lowersurfaces. The method may also include the additional step of affixingimmobilizing instrumentation to the vertebral bones of the patient tohold the restored vertebral bones rigidly in position to facilitatefusion, and positioning bone fusion material adjacent to the restoredvertebral bones. It shall be understood that other equivalent (oralternatively efficacious) means for facilitating healing, such asincluding positioning a non-fusion intervertebral spacer device betweenthe restored vertebral bones so that a proper anatomical motion may bepossible.

The surgical treatment set forth above should be further refinedinasmuch with respect to the diametrically tapered cylindrical spacerelements, such that each has a width along its central cylindrical axissubstantially equivalent to the axial width of the final cylindricalspacer element utilized in the step of sequentially inserting andremoving the series of progressively wider cylindrical spacer elementsto restore the proper anatomical spacing between the pair of adjacentvertebral bones.

It shall be understood that each progressively wider cylindrical spacerelement and/or diametrically tapered cylindrical spacer element maycomprise solid or porous metal, or a porous or non-porous organicimplantable material.

For clarity, this embodiment of the surgical method includes exposing anintervertebral space between adjacent vertebral bones, distracting thespace by sequentially inserting therein and subsequently removingtherefrom a plurality of intervertebral spacers, each having apredetermined thickness, the thicknesses incrementally increasing fromone spacer to another at an increment acceptable for safely distractingthe space to a desired distance, and when adjustment of an angularmisalignment of the adjacent vertebral bones is necessary, inserting,and when necessary rotating, in the intervertebral space, at least onediametrically tapered intervertebral spacer having a thickness along itscentral cylindrical axis sufficient to maintain the desired distancebetween the adjacent vertebral bones, and a diametrical angle sufficientto reorient the adjacent bones to the desired configuration, whenrotational adjustment of the angular misalignment is necessary, rotatingsaid tapered intervertebral spacer within the space until the desiredalignment is established.

In an alternative embodiment, in which porous spacers are utilized, thesurgical method of the present invention may comprise: determining anangular misalignment associated with at least one pair of adjacentvertebral bones; sequentially inserting and removing a series ofprogressively wider cylindrical spacer elements into the correspondingintervertebral space between said at least one pair of adjacentvertebral bones until the proper anatomical spacing between the pair ofadjacent vertebral bones is restored; for each intervertebral space,inserting a diametrically tapered cylindrical porous spacer element intothe intervertebral space between said corresponding pair of adjacentvertebral bones; rotating said diametrically tapered cylindrical porousspacer element such that the rotational orientation of the taperedcylindrical porous spacer element introduces the appropriate counteroffset to the intervertebral space of the previously misalignedscoliotic vertebral bones, thereby restoring the proper anatomicalalignment of the vertebral bones; and stabilizing the pair of adjacentvertebral bones to permit infused growth of bone into the diametricallytapered cylindrical porous spacer element.

As shall be readily understood, in its most basic form, the method ofthe present invention principally consists of sequentially inserting andremoving a series of progressively wider cylindrical spacer elementsinto the intervertebral space between adjacent vertebral bones until thedistance between the vertebral bones is anatomically appropriate.

More particularly, with respect to the various spacers of the presentinvention, in its most basic form, the spacers comprise a plurality ofsequentially axially wider disc spacer elements, the sequentialinsertion and removal of which, into an intervertebral space effects awidening of the intervertebral space, such that a desired anatomicalspacing of adjacent vertebral bones may be restored. These spacers mayinclude beveled upper and lower circumferential radial edges whichfacilitate the application of the desired spreading force to theadjacent vertebral bones. For the ease of surgical use, these spacersmay each include an engagement locus which couples with a correspondinginsertion and removal tool to facilitate the same. This locus comprisesan axially medial groove into which said insertion and removal tool canbe seated. In two alternative embodiments, the medial groove maycomprises a constant width, such that each disc spacer element mayrotate freely within the corresponding insertion and removal tool.Alternatively, the groove may be a radially widening groove, such thateach disc spacer element may be prevented from rotating freely withrespect to the corresponding insertion and removal tool by a clampingaction thereof, thereby permitting the controlled rotation of thecorresponding disc spacer element within the intervertebral space bymanipulation of the insertion and removal tool.

Tapered spacers, for use in reorienting as well as distracting thealignment of the adjacent vertebral bones may be used. These taperedspacers comprise diametrically tapered upper and lower surfaces.Ideally, for surgeon measurement purposes, each of the disc spacerelements includes at least two relative angle designation marks on atleast one of said upper and lower surfaces such that a surgeon user mayreadily visually determine the rotational angle of said disc spacerelement relative to a known reference.

It shall be understood that the intervertebral spacers each have aunique axial thickness, the thicknesses increasing sequentially from onespacer to another, the increasing thicknesses increasing incrementally,said plurality of spacers being particularly useful for graduallydistracting adjacent vertebral bones in an anatomically appropriatemanner.

A critical feature of the present invention is the potential for usingporous spacers to distract and potentially reorient the spine, and thatthe spacers may be implanted permanently into the space between thevertebral bones such that bone ingrowth and solid fusion may occuracross the intervertebral space.

As introduced above, insertion tools are additional components of thepresent invention. In a first embodiment, the instrument for insertingand removing an intervertebral spacer into and out from anintervertebral space between adjacent vertebral bones, the spacer havinga trunk portion having a longitudinal axis and flange portions at eachlongitudinal end of the trunk, the instrument comprises: a shaft havinga proximal end and a distal end; said proximal end including a handle;and a holding structure provided at the distal end, which holdingstructure includes an enclosure within which the trunk of the spacer maybe selectively introduced and maintained therein, the holding structurehaving an opening leading to the enclosure and through which opening thetrunk of the spacer may be selectively passed to when forcedtherethough. More specifically, the trunk of the spacer has a firstwidth, the opening has a second width which is incrementally smallerthan the first width, and the enclosure has a third width whichaccommodates the first width, such that selective introduction of thetrunk through the opening and into the enclosure requires a force toelastically widen the opening such that the trunk may pass through theopening and into the enclosure, the restoration of the opening providingan occlusion which maintains the trunk within the enclosure. Assuggested above, the trunk is generally cylindrical and, therefore, theholding structure includes a hook having a curvate extent which forms apartial-circular enclosure, and which curvate extent fits between theflanges when the trunk is maintained within the enclosure.

In such an embodiment, the intervertebral spacer is selectively snappedinto and out of the enclosure through the opening, and such that theintervertebral spacer may be rotationally freely held within theenclosure. In order to snap the spacer into and out of the enclosure, asecond element is often utilized. This second helper tool comprises ahandle portion at one end, and a bifurcated pair of spaced apart curvatehook-shaped tines at the other. The times have a radius of curvaturegreater than that of each of the spacers, such that when the first andsecond elements engage one another (at a fulcrum point at the point ofbifurcation of the spaced apart curvate hook-shaped tines and a pointbetween the handle and enclosure ends of the first element), theintroduction and removal of the distraction member from the enclosure isfacilitated.

In a second embodiment, which is more suited for the insertion, rotationand removal of the tapered spacers, the tool comprises a shaft having aproximal end and a distal end, said proximal end forming a handle andthe distal end forming a spacer member engaging subassembly; said spacermember engaging subassembly including at least one selectively expandingand contracting enclosure into which the central core may be introducedwhen the engaging subassembly is in the expanded state, and which holdsthe spacer member so that it cannot move when the selectively expandingand contracting enclosure is rendered into the contracted state; and anactuating mechanism, extending from the proximal end to the distal end,by which the spacer member engaging subassembly may be selectivelyexpanded and contracted. More specifically, the spacer member engagingsubassembly comprises a fixed curvate hook defining a portion of theenclosure, a second, selectively advanceable and retractable, portionadjacent the fixed hook portion and said first and second portionsforming said selectively expanding and contracting enclosure. Statedalternatively, the selectively expanding and contracting enclosure isformed by at least two members which are maintained in selectivelyslideable association with each other, at least one of said at least twomembers including a tapered edge thereof.

The instrument of this embodiment includes an actuating mechanismincluding a trigger element disposed in the handle portion, whichtrigger is actionably coupled to advancing and retracting cams which arecoupled to the second portion to advance and retract the second portionin accordance with selective manipulation of the trigger. In moredetail, the spacer member engaging subassembly comprises a fixed memberand a selectively moveable member which, together, form said selectivelyexpanding and contracting enclosure, and wherein said actuatingmechanism comprises a trigger which is mechanically coupled to saidselectively moveable member, the mechanical coupling including a rod, aplate having a protrusion, and a lever having a slot, the rod beingconnected at one end to the selectively moveable member and at anotherend to the plate, the protrusion engaging the slot, the lever beingattached to the trigger, so that when the trigger is engaged, the leverpulls the plate protrusion by the slot, the plate pulls the rod, and therod moves the selectively moveable member toward the fixed member.

In a third embodiment, the tool comprises a shaft having a proximal endforming a handle, and a distal end forming a claw subassembly forholding said spacer, said claw subassembly including a first pincerwhich is fixed at the distal end of the shaft and a second pincer whichis selectively rotateable into and out of spacer holding associationwith said first pincer to hold and release, respectively, the spacer;and an actuation mechanism for selectively rotating the second pincer.The second pincer is rotateably mounted to the shaft and is springbiased away from the first pincer.

In this embodiment the actuation mechanism comprises a sliding membermounted to the shaft which is selectively moveable in the distaldirection by a force sufficient to overcome the bias of the spring, thedistally directed movement of the sliding member thereby causing thesecond pincer to move toward the fixed first pincer, and the subsequentretraction of the sliding member in a proximal direction causes thesliding member to disengage the second pincer and the permits thepincers to separate under the bias of the spring. In order to facilitatethis action, the second pincer includes a tapered surface which isengaged by a corresponding surface of the sliding member, saidengagement causes the second pincer to rotate relative to the firstpincer.

More specifically, the intervertebral spacer comprises a cylindricalmember having an annular groove defining a central axial core portionand a pair of flange portions at opposing ends thereof; and the clawsubassembly engages the spacer at the central axial core.

Stated alternatively, this third embodiment comprises a pair of pincers,a first of this pair being fixed, and a second being coupled to thefirst in open-biased opposition thereto, and a sliding element which maybe selectively translated into and out of engagement with said secondpincer to close and open the pair of pincers, respectively. The pair ofpincers define an intervertebral spacer grasping enclosure having anaccess opening through which the intervertebral spacer can be passed forplacement into the enclosure when the sliding element is out ofengagement with the second pincer, and the spacer is securely maintainedbetween the first and second pincers when the sliding element has beentranslated into engagement with the second pincer. Ideally, the firstand second pincers are mounted at the distal end of a common shaft, andthe sliding element is translateable along said shaft; and wherein thesecond pincer has a portion thereof which is engaged by the slidingelement to close the pair of pincers. In addition, the second pincer ismounted to the common shaft by a pivot joint, and the portion of thesecond pincer which is engaged by the sliding element is a taperedsurface, the angle of which tapered surface, when engaged by the slidingelement, causes the second pincer to rotate about the pivot joint,closing the first and second pincers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a-c illustrates a first embodiment of an intervertebral trialspacer of the invention is illustrated in side, top and side cutawayviews, respectively.

FIG. 1 d illustrates a first set of intervertebral spacers of theinvention in a side view.

FIGS. 2 a-c illustrate a second embodiment of an intervertebral spacerof the invention in side, top and side cutaway views, respectively.

FIG. 2 d illustrates a second set of intervertebral spacers of theinvention in a side view.

FIGS. 3 a-c illustrate a third embodiment of an intervertebral spacer ofthe invention in side, top and side cutaway views, respectively.

FIG. 3 d illustrates a third set of tapered intervertebral spacers ofthe invention in a side view.

FIGS. 4 a-c illustrate a fourth embodiment of an intervertebral spacerof the invention in side, top and side cutaway views, respectively.

FIG. 4 d illustrates a fourth set of tapered intervertebral spacers ofthe invention in a side view.

FIG. 5 a illustrates a first embodiment of a spacer insertion tool 500of the invention in a side view.

FIG. 5 b is a cutaway view of the insertion tool of FIG. 5 a holding thespacer of FIGS. 1 a-c.

FIGS. 6 a-b illustrates an embodiment of a loading accessory for aspacer insertion tool of the invention in side and top views,respectively.

FIG. 6 c shows the loading accessory of FIGS. 6 a-b in operation to loadthe spacer of FIG. 1 a-c into the spacer insertion tool of FIG. 5 a.

FIG. 6 d shows the loading accessory of FIGS. 6 a-b in operation tounload the spacer the spacer insertion tool of FIG. 5 a.

FIG. 7 a illustrates another embodiment of a spacer insertion tool ofthe invention in a side view.

FIG. 7 b is a cutaway view of the insertion tool of FIG. 7 a holding thespacer of FIGS. 4 a-c.

FIGS. 8 a-b illustrates yet another embodiment of a spacer insertiontool of the invention in open and closed side views, respectively.

FIG. 8 c is a cutaway view of the insertion tool of FIGS. 8 a-b holdingthe spacer of FIGS. 4 a-c.

DETAILED DESCRIPTION OF THE INVENTION

While the present invention will be described more fully hereinafterwith reference to the accompanying drawings, in which particularembodiments and methods of implantation are shown, it is to beunderstood at the outset that persons skilled in the art may modify theinvention herein described while achieving the functions and results ofthis invention. Accordingly, the descriptions which follow are to beunderstood as illustrative and exemplary of specific structures, aspectsand features within the broad scope of the present invention and not aslimiting of such broad scope. Like numbers refer to similar features oflike elements throughout.

First, the patient spine is exposed through an anterior approach (i.e.the surgeon creates an access hole which permits direct interaction withthe anterior and/or anterio-lateral portion of the intervertebralbodies). In the case of scoliosis, as well as in other disorders inwhich the intervertebral space requires distraction and/orrepositioning, the surgeon removes the intervertebral disc material,usually leaving some portion of the annulus (the cylindrical weave offibrous tissue which normally surrounds and constrains the softercartilage cushion of the disc material). The surgeon then, insuccession, inserts a series of intervertebral trial spacers of definedwidth. Each of the series of spacers is of a progressively widerthickness, resulting in the continual widening of the space untilrestoration of the proper disc height has been achieved. Proper discheight restoration is determined by surgical experience, and byobservation of the annulus. (Often, the tightening of the annulusindicates that the proper disc height has been reached, inasmuch as theannulus is much less likely to be distorted by the same disruption thatcaused the intervertebral disc to collapse in the first place.)

More particularly, with respect to the specific instruments disclosedherein, a series of solid trial spacer elements and an instrument fortheir insertion and removal is now provided. Each trial spacer is agenerally cylindrical disc having a deep annular groove at its midpoint,which forms a central trunk and radial flanges at each end of the trunk.Stated alternatively, two cylindrical upper and lower halves of the discare held in a closely coaxial spaced apart association by the centraltrunk, which forms a coaxial bridge between the upper and lower halves.The annular groove is particularly useful for holding the spacer usingthe spacer insertion instrument of the invention, described below, inthat the holding end of the insertion instrument fits within the groove.

A variety of features of embodiments of the trial spacer elements aredisclosed. In some embodiments, such as the first and second embodimentsdescribed below, support portions (the portions that are in contact withthe adjacent vertebral bodies when the spacer is disposed between thebodies) of the top and bottom surfaces are parallel. Spacers having thisfeature are generally described herein as “constant thickness” trialspacers. In other embodiments, such as the third and fourth embodimentsdescribed below, the support portions are not parallel, providing anoverall taper to the spacer at an angle. Spacers having this feature aregenerally described herein as “tapered thickness” trial spacers. Thetapered thickness trial spacers are particularly useful for treatingscoliosis, as described below.

Other features of embodiments of the trial spacer elements includebeveled flanges and non-parallel annular groove walls. Morespecifically, in some embodiments, such as the second and fourthembodiments described below, the flanges are radially beveled in that anouter edge of the top surface of the disc is tapered toward an outeredge of the bottom surface of the disc. In other embodiments, such asthe first and third embodiments described below, the flanges are notradially beveled in this manner. The radial beveling feature can beparticularly useful for easing the insertion of the spacer in betweencollapsed vertebral bodies, as described below. Further, in someembodiments, such as the first and third embodiments described below,the walls of the annular groove are parallel, such that the floor of thegroove is as wide as the opening of the groove. In other embodiments,such as the second and fourth embodiments described below, the walls ofthe annular groove are tapered toward one another with the increasingdepth of the groove, such that the floor of the groove is narrower thanthe opening of the groove. Each type of annular groove is useful,depending on the particular surgical application and on the particularembodiment of the spacer insertion instrument that is used to insert thespacer.

Collections of trial spacer elements are provided by the invention.Preferably, each spacer in a particular set maintains the same diameteras the other spacers in the set. (It shall be understood that differentcollections of spacers may be provided such that the diameter of theselected collection of trial spacers is appropriate for the specificpatient being treated. For example, the diameters of the trial spacersin a collection that is suitable for use with pediatric patients wouldbe smaller than the diameters of the trial spacers in a collection thatis suitable for use with adult patients.) Also preferably, each spacerin a particular set has a predetermined depth that differs from thedepth of the other spacers in the set. The predetermined depth isprovided in that while each spacer in the set shares the same annulargroove dimensions (so that each can be held by the same insertioninstrument), each spacer has a different flange thickness (in sets wherethe spacers are constant thickness spacers). For sets of taperedthickness spacers, the predetermined maximum depth and predeterminedminimum depth (the two depths providing the overall taper) are providedin that while each spacer in the set shares the same annular groovedimensions (so that each can be held by the same insertion instrument),each spacer has a different maximum flange thickness and a differentminimum flange thickness. Preferably in sets of tapered thicknessspacers, the overall taper angle is the same for each spacer in the set.The usefulness of providing sets of spacers similar in most respectsexcept for the depth dimension will be described in greater detailbelow.

Referring now to FIGS. 1 a-c, a first embodiment of an intervertebraltrial spacer 100 of the invention is illustrated in side, top and sidecutaway views, respectively. The spacer 100 is a cylindrical disc withan annular groove 102 that forms a central trunk 103 and radial flanges104,106 at each end of the trunk 102. In this embodiment, supportportions 108,110 of the top and bottom surfaces 112,114 of the disc areparallel. Further in this embodiment, the walls 120,122 of the annulargroove 102 are parallel, such that the floor 124 of the groove 102 is aswide as the opening 126 of the groove 102. Further in this embodiment,the spacer 100 has a central bore 128.

Referring now to FIG. 1 d, a set of intervertebral spacers 100 a-l ofthe invention are illustrated in a side view. Each spacer 100 a-l isformed generally similarly to the intervertebral spacer 100 of FIGS. 1a-c, except that each spacer 100 a-l has a predetermined depth (denotedby the preferred dimension identified adjacent each spacer) provided inthat while each spacer 100 a-l shares the same annular groove dimensionsas the other spacers, each spacer 100 a-l has a different flangethickness dimension. For example, the flanges 104 l,106 l are thickerthan the flanges 104 a,106 a.

Referring now to FIGS. 2 a-c, a second embodiment of an intervertebralspacer 200 of the invention is illustrated in side, top and side cutawayviews, respectively. Similarly to the spacer 100, the spacer 200 is acylindrical disc with an annular groove 202 that forms a central trunk203 and radial flanges 204,206 at each end of the trunk 202. However, inthis embodiment, the flanges 204,206 are radially tapered in thatsupport portions 208,210 of the top and bottom surfaces 212,214 of thedisc are parallel, while an outer edge 216 of the top surface 212 istapered toward an outer edge 218 of the bottom surface 214. Further inthis embodiment, in contrast to the spacer 100, the walls 220,222 of theannular groove 202 are tapered toward one another with the increasingdepth of the groove 202, such that the floor 224 of the groove 202 ismore narrow than the opening 226 of the groove. Further in thisembodiment, the spacer 200 has a central bore 228.

Referring now to FIG. 2 d, a set of intervertebral spacers 200 a-l ofthe invention are illustrated in a side view. Each spacer 200 a-l isformed generally similarly to the intervertebral spacer 200 of FIGS. 2a-c, except that each spacer 200 a-l has a predetermined depth (denotedby the preferred dimension identified adjacent each spacer) provided inthat while each spacer 200 a-l shares the same annular groove dimensionsas the other spacers, each spacer 200 a-l has a different flangethickness dimension. For example, the flanges 204 l,206 l are thickerthan the flanges 204 a,206 a.

With regard to the instrument for the insertion and removal of the trialspacer elements, a first embodiment (particularly useful for insertingconstant thickness trial spacers) of a spacer insertion tool includes anelongated shaft and a handle at one end of the shaft. The distal end ofthe shaft includes semi-circular hook that is adapted to hold a trialspacer within an enclosure formed by the hook. The angle swept out bythe hook is slightly greater than 180 degrees, but the inner diameter ofthe hook is only slightly larger than the central trunk of the trialspacer. Therefore, the trial spacer may be snapped into the enclosure,but maintains complete rotational freedom within its grasp. A loadingtool may be provided to assist in the loading and unloading of the trialspacer from the trial spacer insertion instrument of this embodiment.This loading tool comprises a forked hook having two tines separated bya notch that engages the shaft of the insertion tool as the tines engagethe flanges of the trial spacer, to force the trial spacer into theenclosure. Alternatively and/or additionally, the same device may beutilized to remove the spacer from the enclosure, by reversing theposition of the forked hook relative to the insertion tool and thespacer.

Referring now to FIG. 5 a, a first embodiment of a spacer insertion tool500 of the invention is illustrated in a side view. The insertion tool500 includes an elongated shaft 502 and a handle 503 at one end of theshaft 502. At the other end of the shaft 502, the insertion tool 500includes a semi-circular hook 504 that is adapted to hold anintervertebral spacer of the invention within an enclosure 506 of thehook 504. The central trunk of the spacer can be snapped into theenclosure 506 of the hook 504 so that the extent of the hook 504 fitsloosely within the annular groove of the spacer and is flanked by theflanges of the spacer. The central trunk of the spacer can also besnapped out of the enclosure 506.

In this regard, the hook 504 has an opening 508 that temporarily expandswhen the central trunk of the spacer is forced through the opening 508.That is, the outer diameter of the central trunk is greater than thewidth of the opening 508, so that the central trunk cannot pass throughthe opening 508 without force. The application of a force sufficient tocause the opening 508 to expand when confronted with the central trunkcauses the central trunk to pass through the opening 508. After thecentral trunk has cleared the opening 508, the opening 508 willcontract. The temporary expansion in this embodiment is provided by thehook 504 being formed of a material having a low elasticity and the hook504 being provided with a stress notch 510 on the extent (preferablylocated opposite the opening 508 for maximum efficiency) to ease theexpansion.

Once the spacer is loaded into the enclosure, the opening 508, havingcontracted back to its resting width, prevents the central trunk fromexiting the enclosure radially through the opening, because, as statedabove, the outer diameter of the central trunk is greater than the widthof the opening 508. Further, by flanking the extent of the hook 504, theflanges of the spacer prevent the spacer from exiting the enclosurelaterally. The hook 504 therefore holds the spacer loosely in theenclosure so that the spacer can rotate about the cylindrical axis ofthe central trunk while being held by the hook 504.

Referring now to FIG. 5 b, a cutaway view of the insertion tool 500 ofFIG. 5 a holding the spacer 100 of FIGS. 1 a-c shows the extent of thehook 504 in cross-section and fitting within the annular groove of thespacer. It can be seen that to enable the spacer 100 to be loosely heldin the enclosure, the width of the extent is smaller than the width ofthe annular groove, and the depth of the extent is less than the depthof the annular groove if it is desirable for the flanges to fully flankthe extent. Preferably, as shown, the outer diameter of the hook 504 issubstantially equal to the outer diameter of the spacer 100.

Referring now to FIG. 6 a-b, an embodiment of a loading accessory 600for a spacer insertion tool of the invention is illustrated in side andtop views, respectively. The loading accessory 600 can be used to easethe passing of the central trunk of the spacer through the opening ofthe spacer insertion tool, both for loading the spacer into theenclosure and unloading the spacer from the enclosure. The loadingaccessory 600 includes an elongated shaft 602 and a forked hook 604 atan end of the shaft 602. A notch 606 having a base 608 separates thetines 610,612 of the forked hook 604.

The width of the notch 608 separating the tines 610,612 is wide enoughto accommodate the width of the hook 504 of the insertion tool 500 andthe width of the shaft 502 of the insertion tool 500, but narrow enoughso that the tines 610,612 can engage the edges of the flanges of thespacer. Preferably, as shown, the curvature of the tines 608,610 followsthe curvature of the edges of the flanges.

Referring now to FIG. 6 c, the loading accessory 600 of FIGS. 6 a-b isshown in operation to load the spacer 100 of FIG. 1 a-c into the spacerinsertion tool 500 of FIG. 5 a. Initially, the spacer 100 is positionedadjacent the opening 508 of the insertion tool 500. Then, the tines610,612 of the loading accessory 600 are passed on either side of theshaft 502 of the insertion tool 500 such that the notch 606 accommodatesthe shaft 502 and until the base 608 of the notch 606 contacts the shaft502. Then, the loading accessory 600 is rotated, using the contactbetween the shaft 502 and the base 608 as a fulcrum, to cause the tines610,612 to engage the flanges 104,106 of the spacer 100 and push theminto the enclosure 506 of the tool 500. Applying a force to therotation, sufficient to cause the opening 508 of the tool 500 to expandwhen confronted with the central trunk of the spacer, causes the centraltrunk to pass through the opening 508.

Referring now to FIG. 6 d, the loading accessory 600 of FIGS. 6 a-b isshown in operation to unload the spacer 100 of FIG. 1 a-c from thespacer insertion tool 500 of FIG. 5 a. Initially, with the spacer 100held by the tool 500, the tines 610,612 of the loading accessory 600 arepassed on either side of the shaft 502 of the insertion tool 500 suchthat the notch 606 accommodates the shaft 502 and until the base 608 ofthe notch 606 contacts the shaft 502. Then, the loading accessory 600 isrotated, using the contact between the shaft 502 and the base 608 as afulcrum, to cause the tines 610,612 to engage the flanges 104,106 of thespacer 100 and push them out of the enclosure 506 of the tool 500.Applying a force to the rotation, sufficient to cause the opening 508 ofthe tool 500 to expand when confronted with the central trunk of thespacer, causes the central trunk to pass through the opening 508. Thewidth of the notch 606 accommodates the width of the hook 504 as thespacer 100 is being pushed out of the enclosure 506.

The insertion tool of this embodiment, can be used to insert a series ofconstant thickness trial spacers (some of which may have beveled flangeedges for easing the insertion between the collapsed bones and into thespace to be distracted). More specifically, thinner trial spacers caninitially be inserted into the spacer, followed successively by thickertrial spacers until the desired spacing is achieved. Once theappropriate spacing has been achieved, immobilization of the spine byfixation, fusion, or non-fusion techniques and devices, such as thoseset forth in co-pending U.S. patent application Ser. Nos. 09/906,117 and09/906,118, entitled “An Intervertebral Spacer Device Having a WaveWasher Force Restoring Element” and “An Intervertebral Spacer DeviceHaving a Spiral Wave Washer Force Restoring Element”, respectively, aswell as U.S. Pat. No. 5,989,291, entitled “An Intervertebral SpacerDevice”, each of which has been assigned to the same assignee as thispresent invention, the specifications of which are all fullyincorporated herein by reference, may be desirable.

While simple distraction to a constant height across the intervertebralspace is appropriate for standard disc compression pathologies, in thecase of scoliosis, simple constant thickness distraction is insufficientto remediate the pathological condition. What is necessary is thedistraction of the sequence of spaces, each to an appropriate angle andheight, such that the overall spinal configuration is anatomicallycorrect. Tapered trial spacers, such as those disclosed in the presentapplication, are the first such distraction tools to provide such atailored correction of the misangulation of the spinal bones.

More particularly, the surgeon inserts the tapered trial spacers intothe intervertebral space (presumably from the anterior, oranterio-lateral, approach) with the narrow edge of the trial spacerforming a wedge and sliding between the adjacent bones. By utilizingeither a second or third embodiment of the spacer insertion tool,described more fully hereinafter with respect to FIGS. 7 a-c and 8 a-crespectively, the surgeon may turn the spacer around its axis within theintervertebral space to find the most appropriate rotational position(corresponding to the most desirable straightening effect on the spinalcolumn). Stated alternatively, each of the tapered trial spacers has anoverall wedge shape that generally corresponds to the pathologicaltapering of the adjacent bones that characterizes scoliosis. By rotatingthe wedge-shaped spacer after it has been placed between the adjacentbones, the overall disc alignment may be compensated, restoringappropriate anatomical status. It should be understood that additionalrotation of the spacer may restore lordosis to the spine, and thatover-rotation (if the particular spine is flexible enough) of the spacerwould result in a pathological curvature in the opposite direction.

Referring now to FIGS. 3 a-c, a third embodiment of an intervertebralspacer 300 of the invention is illustrated in side, top and side cutawayviews, respectively. Similarly to the spacer 100, the spacer 300 is acylindrical disc with an annular groove 302 that forms a central trunk303 and radial flanges 304,306 at each end of the trunk 303. However, inthis embodiment, support portions 308,310 of the top and bottom surfaces312,314 of the disc are not parallel, providing an overall taper to thespacer 300 at an angle. Still, similarly to the spacer 100, the walls320,322 of the annular groove 302 are parallel, such that the floor 324of the groove 302 is as wide as the opening 326 of the groove 302.Further in this embodiment, the spacer 300 has a central bore 328.

Referring now to FIG. 3 d, a set of tapered intervertebral spacers 300a-j of the invention are illustrated in a side view. Each spacer 300 a-jis formed generally similarly to the intervertebral spacer 300 of FIGS.3 a-c, except that each spacer 300 a-j has a predetermined maximum depth(denoted by the preferred maximum depth dimension identified adjacenteach spacer) and a predetermined minimum depth (denoted by the preferredminimum depth dimension identified adjacent each spacer), each providedin that while each spacer 300 a-j shares the same annular groove widthdimension as the other spacers, each spacer 300 a-j has a differentmaximum flange thickness dimension and a different minimum flangethickness dimension. For example, the flanges 304 j,306 j have a thickermaximum flange thickness dimension and a thicker minimum flangethickness dimension than the flanges 304 a,306 a.

Referring now to FIGS. 4 a-c, a fourth embodiment of an intervertebralspacer 400 of the invention is illustrated in side, top and side cutawayviews, respectively. Similarly to the spacer 200, the spacer 400 is acylindrical disc with an annular groove 402 that forms a central trunk403 and radial flanges 404,406 at each end of the trunk 403. However, inthis embodiment, support portions 408,410 of the top and bottom surfaces412,414 of the disc are not parallel. Still, similarly to the spacer200, the flanges 404,406 are radially tapered in that an outer edge 416of the top surface 412 is tapered toward an outer edge 418 of the bottomsurface 414. Further in this embodiment, similarly to the spacer 200,the walls 420,422 of the annular groove 402 are tapered toward oneanother with the increasing depth of the groove 402, such that the floor424 of the groove 402 is more narrow than the opening 426 of the groove.Further in this embodiment, the spacer 400 has a central bore 428.

Referring now to FIG. 4 d, a set of tapered intervertebral spacers 400a-j of the invention are illustrated in a side view. Each spacer 400 a-jis formed generally similarly to the intervertebral spacer 400 of FIGS.4 a-c, except that each spacer 400 a-j has a predetermined maximum depth(denoted by the preferred maximum depth dimension identified adjacenteach spacer) and a predetermined minimum depth (denoted by the preferredminimum depth dimension identified adjacent each spacer), each providedin that while each spacer 400 a-j shares the same annular groove widthdimension as the other spacers, each spacer 400 a-j has a differentmaximum flange thickness dimension and a different minimum flangethickness dimension. For example, the flanges 404 j,406 j have a thickermaximum flange thickness dimension and a thicker minimum flangethickness dimension than the flanges 404 a,406 a.

It should understood that the various features of the differentembodiments of the intervertebral spacer of the invention discussedabove can be used in various combinations and permutations to form theillustrated embodiments and other embodiments of the intervertebralspacer of the invention. In some embodiments, the walls of the annulargroove are parallel. In other embodiments, they are not parallel. Insome embodiments where they are not parallel, they are tapered towardone another with the increasing depth of the groove. In otherembodiments where they are not parallel, they are tapered toward oneanother with the decreasing depth of the groove. In some embodiments,the support portions of the top and bottom surfaces are parallel. Inother embodiments, they are not parallel. In some embodiments, theflanges are radially tapered in that the outer edge of the top surfaceis tapered toward an outer edge of the bottom surface. In otherembodiments, the flanges are not radially tapered. In some embodiments,the spacer has a central bore. In other embodiments, the spacer does nothave a central bore.

It should be understood that while in the illustrated embodiments wherespacers in a set have an overall taper, the angle of the overall taperof each spacer in the set is the same as the angle of the overall taperof the other spacers in the set, the invention encompasses a set ofspacers in which the angle of the overall taper of each spacer in theset is different than the angle of the overall taper of at least oneother spacer in the set.

It should be understood that while in the illustrated embodiments wherethe spacer has an overall taper, the angle of the overall taper can bepredetermined, such that the maximum flange thickness and the minimumflange thickness can be selected to achieve a desired overall taperangle.

It should be understood that while in the illustrated embodiments thespacers are shown as having a cylindrical shape, it should be understoodthat in other embodiment, the spacers can have oval, square, orrectangular cross-sections, or cross-sections of other shapes, providedthat any corners are rounded as necessary to prevent damage tosurrounding tissue.

As suggested previously, the insertion, rotation and removal of thetapered trial intervertebral spacers requires an alternate spacerinsertion tool. This second embodiment of the spacer insertion toolincludes a handle and an elongated dual shaft, the dual shaftculminating in a trial spacer grasping pincer, rather than the simplehook of the first embodiment. This pincer differs from the hook of thefirst embodiment of the trial spacer insertion tool described above,inasmuch as the dual shaft includes a fixed shaft and a selectivelyengagable shaft which, together, form pincer. More specifically, thefixed shaft includes a semicircular hook portion of the pincer at itsdistal end, having an enclosure within which a trial spacer can beplaced. The selectively engagable shaft includes the complementaryportion of the pincer, which moves toward the hook portion to grasp andhold the trial spacer when the engagable shaft is engaged, and movesaway from the hook portion to release the trial spacer when theengagable shaft is disengaged. (The spacer can be unloaded and loadedwhen the engagable shaft is disengaged.) The engagement action preventsthe spacer from moving relative to the tool, and therefore permits thesurgeon to rotate the tapered spacer in between the vertebral bodies (bycontrast, the first embodiment of the trial spacer insertion instrumentpermitted the spacer to rotate freely in the enclosure of the hook).

Referring now to FIG. 7 a, another embodiment of a spacer insertion tool700 of the invention is illustrated in a side view. The insertion tool700 includes an elongated shaft 702 and a handle 704 at one end of theshaft 702. The insertion tool 700 further includes a compressionassembly that is adapted to hold an intervertebral spacer of theinvention at the other end of the shaft 702 so that the spacer cannotmove when held. The insertion tool 700 further includes a releaseassembly that is adapted to release the spacer from being held.

The compression assembly includes a semicircular hook 706 at the otherend of the shaft 702 and a compression surface 708 adjacent the hook706. The hook 706 has an enclosure 709 defined by the extent of the hook706 and an opening 710 through which the central trunk can pass freelyto be placed into the enclosure 709. That is, the width of the opening710 is greater than the diameter of the central trunk. When the centraltrunk is placed within the enclosure 709, the extent of the hook 706fits loosely within the annular groove of the spacer.

The compression assembly further includes a compression trigger 712mechanically connected to the hook 706 such that as the compressiontrigger 712 is placed in an engaged position, the hook 706 is pulledtoward the compression surface 708. The mechanical connection includes arod 714 connected at one end to the hook 706 and at the other end to aplate 716. A rod 718 protruding from the plate 716 is engaged by a slot720 in a lever 722 attached to the compression trigger 712. When thecompression trigger 712 is engaged, the rod 714 of the lever 722 pullsthe plate 716 by the slot 720. The plate 716 in turn pulls the rod 714,which in turn pulls the hook 704 toward the compression surface 708.

When the hook 706 is pulled toward the compression surface 708 when thecentral trunk of the spacer is in the enclosure 709, the central trunkis compressed within the enclosure 709 between the hook 706 and thecompression surface 708 so that the spacer cannot move.

The release assembly includes a spring 724 biasing the compressiontrigger 712 to a disengaged position. Therefore, after the compressiontrigger 712 is released, it moves to the disengaged position. However,so that the central trunk remains compressed within the enclosure evenafter the compression trigger 712 is released (e.g., so that the surgeondoes not need to continue holding the compression trigger 712 to effectthe compression), the compression assembly further includes teeth 726 onthe rod 714 and corresponding teeth 730 that confront the rod teeth 726to prevent the rod 714 from retreating, to maintain the compression.

The release assembly further includes a release trigger 732 that can beengaged to release the rod teeth 726 from the corresponding teeth 730 toallow the rod 714 to return to its rest position, thereby alleviatingthe compression. More specifically, the release trigger 732 has thecorresponding teeth 730 and the release assembly further includes aspring 734 that biases the release trigger 732 toward a position inwhich the corresponding teeth 730 engage the rod teeth 726. Thisarrangement allows the release trigger 732 to be engaged by pressing therelease trigger 732 with a force great enough to overcome the bias ofthe spring 734, so that the corresponding teeth 730 are disengaged fromthe rod teeth 726. Therefore, when the release trigger 732 is pressed,the compression is alleviated, and the central trunk of the spacer canbe freely passed through the opening 710 to be taken out of theenclosure 709.

Referring now to FIG. 7 b, a cutaway view of the insertion tool 700 ofFIG. 7 a holding the spacer 400 of FIGS. 4 a-c shows the extent of thehook 706 in cross-section and fitting within the annular groove of thespacer as the spacer is compressed between the compression surface 708and the hook 706. It can be seen that the width of the extent of thehook 706 is smaller than the width of the annular groove, and the depthof the extent is less than the depth of the annular groove if it isdesirable for the flanges to fully flank the extent. Preferably, asshown, the outer diameter of the hook 706 is substantially equal to theouter diameter of the spacer 400.

Referring now to FIGS. 8 a-b, yet another embodiment of a spacerinsertion tool 800 of the invention is illustrated in open and closedside views, respectively. The insertion tool 800 includes an elongatedshaft 802 and a handle 804 at one end of the shaft 802. The insertiontool 800 further includes a compression assembly that is adapted to holdan intervertebral spacer of the invention at the other end of the shaft802 so that the spacer cannot move when held. The insertion tool 800further includes a release assembly that is adapted to release thespacer from being held.

The compression assembly includes a claw 806 at the other end of theshaft 802 having opposing pincers 807 a, 807 b, each providing one ofopposing compression surfaces 808 a, 808 b. The claw 806 has anenclosure 809 defined by the extents of the pincers 807 a, 807 b and anopening 810 through which the central trunk can pass freely to be placedinto the enclosure 809 when the claw 806 is open (i.e., when theopposing pincers 807 a, 807 b are separated). That is, the width of theopening 810 is greater than the diameter of the central trunk when theclaw 806 is open. When the central trunk is placed within the enclosure809, the extents of the pincers 807 a, 807 b fit loosely within theannular groove of the spacer.

The compression assembly further includes a compression slide 812 thatwhen moved to an engaged position (here, a forward position shown inFIG. 8 b) closes the claw 806. The closure of the claw 806 by thecompression slide 812 is effected as follows. One of the pincers 807 ais in a fixed position relative to the elongated shaft 802 whereas theother pincer 807 b is adapted to rotate about an axis transverse to theshaft 802. In this embodiment, the rotation is provided by a pin 813passing through each pincer at a rotation point along the transverseaxis. One position of the movable pincer 807 b along the rotation path(shown in FIG. 8 a) defines the opened claw 806 in that the pincers 807a, 807 b are separated. Another position of the movable pincer 807 balong the rotation path (shown in FIG. 8 b) defines the closed claw 806in that the pincers 807 a, 807 b are brought together. When the pincers807 a, 807 b are separated, an engagement surface 814 of the movablepincer 807 b is placed in an available compression path of an engagementsurface 816 of the compression slide 812. The engagement surface 814 istapered so that when the compression slide 812 is moved to the engaged,the engagement surface 816 of the compression slide 812 moves along theavailable compression path and engages the tapered surface 814 to pushthe surface 814 aside and thereby cause a rotation of the movable pincer807 b to the position defining the closed claw 806.

When the pincers 807 a, 807 b are thereby brought together to close theclaw 806 when the central trunk of the spacer is in the enclosure 809,the compression surfaces 808 a, 808 b come to bear on the central trunkto compress it within the enclosure 809 so that the spacer cannot move.

The release assembly includes a spring 818 biasing the movable pincer807 b to the rotation path position defining the open claw 806.Therefore, when the compression slide 812 is moved to a disengagedposition (here, a backward position), the engagement surface 816 of thecompression slide 812 moves along an available release path (here, abacktracking along the compression path) and frees the engagementsurface 814 of the movable pincer 807 b to allow the engagement surface814 to return to a place in the available compression path by thebiasing action of the spring 818. When the claw 806 is open, thecompression is alleviated and the central trunk of the spacer can befreely passed through the opening 810 to be taken out of the enclosure809.

The release assembly further includes at least one barrier 820 a, 820 bthat limits the biasing action of the spring 818 by preventing themovable pincer 807 b from rotating beyond the position that places theengagement surface 814 in the available compression path. In thisembodiment, confrontation surfaces 822 a, 822 b on the movable pincer807 b confront the barriers 820 a, 820 b as the pincer 807 b rotatestoward the rotation path position defining the open claw 806 under thebiasing force of the spring 818. When the engagement surface 814 isreturned to the place in the available compression path, the barriers820 a, 820 b prevent the confrontation surfaces 822 a, 822 b fromadvancing further. The spring 818 and the barriers 820 a, 820 b maintainthe movable pincer 807 b in this position until the compression slide812 is advanced toward the engaged position by a force great enough toovercome the biasing force of the spring 818.

Referring now to FIG. 8 c, a cutaway view of the insertion tool 800 ofFIGS. 8 a-b holding the spacer 400 of FIGS. 4 a-c shows the extents ofthe pincers 807 a, 807 b in cross-section and fitting within the annulargroove of the spacer as the spacer is compressed between the compressionsurfaces 808 a, 808 b. It can be seen that the width of each extent issmaller than the width of the annular groove, and the depth of eachextent is less than the depth of the annular groove if it is desirablefor the flanges to fully flank the extents. Preferably, as shown, theouter diameter of the claw 806 is substantially equal to the outerdiameter of the spacer 400.

There are alternative insertion and rotating instruments that may bedesigned, so long as they selectively and alternatingly release or holdthe trial spacer securely against rotation (the spacer can't rotatefreely if it is to be turned in the intervertebral space). The taperedtrial spacers themselves can include angle markers that clearly indicateto the surgeon the amount of rotation that was necessary for thecorrection of the spinal deformity. Such angle markers can also serve asa guide for the implantation of a secondary bone graft (e.g., a femoralring) or another intervertebral spacer device.

Once the surgeon has determined the appropriate geometry for thesurgical implants via the trial spacers, he or she is ready toimmobilize the spine in that position. While multiple ways forimmobilizing the spine are disclosed in the prior art, any one of whichmay be suitable for the specific surgical patient's treatment, threealternative ways are herein described.

First, the trial spacers may be left in the patient while rod fixationapparatuses (anterior or posterior) are mounted to the spine, therebyholding the spine in its desired orientation even after the trialspacers are subsequently removed. Alternatively, surface plating and/orintervertebral cage devices may be mounted to the spine to promotefusion without the need for bulky rod assemblies. (While this approachmay seem more surgically desirable, questions regarding the long-termstability of these constructs have led to some surgeons to choosecombinations of rodding and cages.)

A third approach to immobilizing the corrected spine is to insert ashaped bone graft, or suitably contoured porous metal spacer, into theproperly distracted intervertebral space, and either plating or usingrod fixation to hold the construct stable as the spine fuses. Theinsertion of a femoral ring allograft, or porous metal implant, into anintervertebral space is described more fully in co-pending U.S. patentapplication Ser. Nos. 09/844,904 and 09/906,123, entitled “A PorousInterbody Fusion Device Having Integrated Polyaxial Locking InterferenceScrews” and “Porous Intervertebral Distraction Spacers”, assigned to thesame assignee as the present invention, the specifications of each beingfully incorporated herein by reference.

The tapered trial spacers may also serve as precursors (measuringinstruments) for another spacer (e.g., a porous metal spacer), similarlyshaped, which is inserted into the intervertebral space by the sameinstrument.

1. A trial spacer kit comprising: a plurality of trial spacers ofvarying heights; each said trial spacer comprising a disc having a topsurface and a bottom surface, a distance between the top and bottomsurfaces defining a height of said spacer, an annular groove formed insaid disc that defines a central trunk of said spacer, the central trunkhaving an upper end and a lower end, a first radial flange provided atthe upper end of the central trunk and a second radial flange providedat the lower end of the central trunk; the annular grooves of each ofsaid trial spacers having a common dimension; the radial flanges of eachof said spacers having a different thickness so that the height of eachsaid spacer is different.
 2. The trial spacer kit as claimed in claim 1,wherein each said disc is substantially cylindrical.
 3. The trial spacerkit as claimed in claim 1, wherein each said spacer has a central boreextending between the top surface and the bottom surface of said disc.4. The trial spacer kit as claimed in claim 3, wherein the central boreextends through the central trunk of each said spacer.
 5. The trialspacer kit as claimed in claim 1, wherein the top and bottom surfaces ofeach said disc are parallel to one another.
 6. The trial spacer kit asclaimed in claim 1, wherein central sections of the top and bottomsurfaces are parallel to one another.
 7. The trial spacer kit as claimedin claim 6, wherein the central sections of the top and bottom surfacesof each said spacer are parallel and an outer edge of the top surface istapered toward an outer edge of the bottom surface.
 8. The trial spaceras claimed in claim 1, wherein the first radial flange has a firstinterior wall and the second radial flange has a second interior wallthat faces the first interior wall, the first and second interior wallsdefining upper and lower limits of said annular groove.
 9. The trialspacer kit as claimed in claim 8, wherein the first and second interiorwalls extend in directions that are parallel to one another.
 10. Thetrial spacer kit as claimed in claim 9, wherein the first and secondinterior walls have sections that are parallel to one another.
 11. Thetrial spacer kit as claimed in claim 8, wherein the first and secondinterior walls taper toward one another between outer edges of saidradial flanges and the central trunk of said spacer.
 12. The trialspacer kit as claimed in claim 1, wherein the top and bottom surfaces ofeach said spacer are substantially flat and non-parallel to one anotherso that each said spacer is tapered between a leading end and a trailingend thereof.
 13. The trial spacer kit as claimed in claim 1, wherein anouter edge of said first radial flange and an outer edge of said secondsaid radial flange are tapered toward one another.
 14. The trial spacerkit as claimed in claim 13, wherein the interior walls that define saidannular groove taper inwardly toward one another between the outer edgesof said radial flanges and the central post, wherein said annular grooveis narrower adjacent the central post and wider adjacent the outer edgesof said radial flanges.
 15. The trial spacer kit as claimed in claim 1,further comprising an instrument for holding each of said spacers duringinsertion and removal into and out from between adjacent vertebralbones, said instrument comprising a shaft having a distal end and aspacer holding structure formed at the distal end, said spacer holdingstructure being adapted to hold said spacers at the annular groovesthereof.
 16. The trial spacer kit as claimed in claim 15, wherein saidinstrument has a longitudinal axis extending along the shaft thereof,said spacer holding structure having an opening for receiving thecentral trunks of said spacers.
 17. The trial spacer kit as claimed inclaim 16, wherein the opening of said spacer holding structure faces adirection that is substantially perpendicular to the longitudinal axisof said instrument.
 18. The trial spacer kit as claimed in claim 15,further comprising a loading tool that facilitates loading and unloadingof said spacers into and out of said holding instrument.
 19. The trialspacer kit as claimed in claim 18, wherein said loading tool comprises ahandle and a bifurcated end, said bifurcated end including a pair ofsimilarly curved tines adapted for engaging said spacers as forces areapplied to said spacers.
 20. The trial spacer kit as claimed in claim19, wherein said holding instrument and said loading tool engage oneanother at a fulcrum point.
 21. The trial spacer kit as claimed in claim1, wherein said spacer holding structure includes a hook adapted to holdsaid spacers at the annular grooves thereof, and wherein said hook has asemi-circular surface that conforms to the annular grooves formed insaid discs.
 22. The trial spacer kit as claimed in claim 1, wherein saidhook is expandable.
 23. The trial spacer kit as claimed in claim 22,wherein said hook includes a notch that enables an opening of said hookto expand and contract.
 24. A trial spacer kit comprising: a pluralityof trial spacers of varying heights; each said trial spacer comprising adisc having a top surface and a bottom surface, a distance between thetop and bottom surfaces defining a height of said spacer, an annulargroove formed in said disc that defines a central trunk of said spacer,the central trunk having an upper end and a lower end, a first radialflange provided at the upper end of the central trunk and a secondradial flange provided at the lower end of the central trunk; theannular grooves of each of said trial spacers having a common dimension;the radial flanges of each of said spacers having a different thicknessso that the height of each said spacer is different; and an instrumentfor holding each of said spacers during insertion and removal into andout from between adjacent vertebral bones, said holding instrumentincluding a hook adapted for holding said spacers at the annular groovesthereof.
 25. A trial spacer kit comprising: a plurality of trial spacersof varying heights; each said trial spacer comprising a disc having atop surface and a bottom surface, a distance between the top and bottomsurfaces defining a height of said spacer, an annular groove formed insaid disc that defines a central trunk of said spacer, the central trunkhaving an upper end and a lower end, a first radial flange provided atthe upper end of the central trunk and a second radial flange providedat the lower end of the central trunk; the annular grooves of each ofsaid trial spacers having a common dimension; the radial flanges of eachof said spacers having a different thickness so that the height of eachsaid spacer is different; a holding instrument including a hook adaptedfor holding said spacers at the annular grooves thereof; and a loadingtool for loading and unloading said spacers into and out of said holdinginstrument.